Take refrigerators, for example. Introduced widely in 1998, inverters doubled energy efficiency, cut energy consumption in half. At prices for electricity and fridges in Japan, you could throw out your old fridge, buy a brand new one and break even on that investment in seven years. I did.
That efficiency is more than free. Beyond the break-even time it pays dividends.
Now, did people mildly interested in a new fridge run out and buy a new one? No, they didn't. Why? Few understand the implications when the label says the product consumes 600 kWh per year when measured according to XYZ standard. My prior fridge would have consumed 1200kWh, had it been measured to the same standard. These 600kWh saved each year is what pays the new fridge - if you keep it for seven years or longer.
Which is the right efficiency product for you right now depends on your specific life circumstances, and a lifetime cost of ownership calculation, plus a risk factor because your life plans may change or new technology may leapfrog prior achievements and offer even more efficiency.